U.S. Pat. No. 4,255,003 discloses a device for connecting a monolithic integrated circuit to a circuit board. The monolithic integrated circuit is mounted on a rectangular ceramic substrate that has connection pads distributed about the periphery of one main face of the substrate. The circuit board has corresponding connection pads exposed at one main face of the board about the periphery of a rectangular "footprint" region corresponding in shape and size to the main face of the ceramic substrate. The circuit board is formed with holes outside the footprint region. A clamping member has four rigid side portions that are connected together and form a rectangular frame. The side portions are formed with an endless groove at the underside of the frame. A frame-like body of elastomeric material projects downwardly from the underside of the clamping member and has a locating ridge that fits in the groove of the clamping member. Strips of conductive material are bonded to the underside of the body of elastomeric material. The elastomeric material is silicone rubber. At each corner, the clamping member has an ear that extends downwardly somewhat beyond the underside of the frame, and each ear is formed with a hole. The circuit board is formed with corresponding holes. Through use of screws extending downwardly through the holes in the ears and the corresponding holes in the circuit board, and nuts engaging the lower ends of the screws, the clamping member may be attached to the circuit board. When the clamping member is so attached, the elastomeric material is compressed and the strips of conductive material provide electrical connection between the connection pads of the substrate and the corresponding connection pads of the circuit board. The compression of the elastomeric material provides contact force between the strips of conductive material and the contact pads.
A practical implementation of the conventional connection device disclosed in U.S. Pat. No. 4,255,003 is designed for use with a substrate that is about 0.64 mm thick. The underside of the frame is stepped, in that the lower surface portion that is inward of the groove is at a height of 1.45 mm above the bottom of the ears and the lower surface portion that is outward of the groove is at a height of 0.81 mm above the bottom of the ears. When seen in cross-section, the body of elastomeric material has two lobes, for engaging the substrate and the circuit board respectively, and each extends 1.02 mm downwards from the relevant surface portion of the frame. When the clamping member is attached to the circuit board and the screws are tightened, each lobe is compressed to a thickness of 0.81 mm, so that the percentage compression of each lobe is about 20%. Of course, manufacturing tolerances result in the percentage compression of the lobes possibly being different from 20%. Nevertheless, the tolerances are sufficiently small, e.g. .-+.0.05 mm on each component, that for all values of the percentage compression permitted by the manufacturing tolerances, adequate contact force is provided between the conductive strips and the pads of the substrate.
In the conventional connection device, the main mechanism for dissipation of heat from the integrated circuit is by conduction downwards through the ceramic substrate into the circuit board. Heat is removed from the bottom face of the circuit board by convection and/or conduction. Circuit board material, e.g. epoxy glass, is a relatively poor conductor of heat, and therefore the practical implementation of the conventional connection device is designed for use with circuit boards no thicker than about 0.64 mm, i.e. single layer circuit boards. It is, however, desirable to be able to use multilayer circuit boards that are about 1.57 mm thick. The high thermal resistance of such a circuit board places a relatively low limit on the amount of power that can be dissipated as heat without causing the temperature of the circuit board to increase excessively and consequently causing damage to the circuit board.